The present invention relates to a lithium secondary battery including an organic electrolyte used for a primary or back-up power source of electronic appliances.
Batteries including an organic electrolyte have a high energy density in general. With the use of such organic electrolyte batteries, therefore, it is possible to make the electronic appliances compact and light and provide them with a long storage characteristic free from a risk of leakage of electrolyte. From the above, there is an increasing demand for such organic electrolyte batteries as a primary or memory back-up power source for various electronic appliances. Main batteries used for such purpose are unchargeable primary batteries. With the remarkable development in handy electronic appliances, however, there has been a great demand currently for the secondary batteries that effectively utilize advantageous characteristics inherent to the organic electrolyte, in order to have more compact and cost-effective electronic appliances free from a burden of laborious maintenance. Under these circumstances, vigorous research and development has been made on the organic electrolyte secondary batteries. Although some of them have been put into practical use, further modification or improvement is still actively continued to have more optimal organic electrolyte secondary batteries.
Conventionally, metallic lithium or an alloy of lithium with lead or aluminum has been focused on as an anode for such organic electrolyte secondary batteries. With the advent of an anode of carbon that intercalates and deintercalates lithium, charge-discharge cycle performance of the batteries has been improved greatly. It was attempted in the Japanese Laid-Open Patent Publication Hei 2-49364 to apply a transition metal oxide for the anode. According to this prior art, the oxide stabilizes the charge-discharge cycle performance of the batteries for a long time.
On the other hand, extensive research has been made on the availability of metal oxides, such as V.sub.2 O.sub.5, Nb.sub.2 O.sub.5, MnO.sub.2, LiCoO.sub.2, LiNiO.sub.2, LiMn.sub.2 O.sub.4 and the like, as cathode active materials that intercalates and deintercalates lithium between crystal layers, crystal lattice positions, or lattice spaces.
Various known electrolytes include lithium salts, such as LiClO.sub.4, LiCF.sub.3 SO.sub.3, LiPF.sub.6 and the like, and mixture solvents comprising propylene carbonate or butylene carbonate and a low viscosity solvent, such as 1,2-dimethoxyethane or dimethyl carbonate.
Various combinations of the above-mentioned anodes, cathode materials and electrolytes can give organic electrolyte lithium secondary batteries with an adequate charge-discharge cycle life. In fact, some of them are in practical use. Although some of the secondary batteries assembled from these combinations seem to have reached a substantially satisfactory level in terms of storage performance, their characteristics as a secondary battery are not enough satisfactory and further improvement in this regard has been hoped for.